During the first five years of the Arctic LTER at Toolik Lake, Alaska, systematic measurements of climate, of tundra plant distribution and productivity, and of lake and stream physics, chemistry and biology were begun. Whole system experiments were set up on the tundra, in streams, and in lakes to examine the ecological effects of changes in environmental and biological factors such as air temperature, added nutrients, and changes in the density of the top predators and grazers. These measurements and long-term experiments are designed to help reach the overall goal: to understand how tundra, streams and lakes function in the Arctic and to predict how they respond to human-induced changes including climate change. Under this broad goal there are three specific goals: (1) Determine year-to-year ecological variability in these systems and measure long-term changes. (2) Understand the extent of control by resources (bottom-up control) or by grazing and predation (top-down control). (3) Measure rates and understand the controls of the exchange of nutrients and organic matter between land and water. Long-term experiments are the heart of the Arctic LTER program. It has been found that arctic systems often do not respond for many years, and that long-term responses are often not predictable from short-term responses. Changes in the responses of both streams and terrestrial vegetation to nutrient amendments are still being documented after 9 years. Lake trout manipulations take many years to show effects as these long-lived fish may change their diet from invertebrates to fish when they reach a certain size. As a result, most long-term experiments and measurements for determining ecological variability will be continued. The results of the long-term experiments will continue to be measured as more is discovered about long-term ecosystem controls by resources and predation. New research on the controls of the exchange of nutrients between land and water will be started. A major watershed experiment will be carried out to measure the movements of water and dissolved gases through the groundwater and into the streams.
